用于开口声辐射控制的虚拟声屏障实现 方法及机理研究*

建筑物通常留有开口以便人员物料的进出及室内的自然通风采光,但这些开口也是噪声传播的途径。传统被动噪声控制方法需要将开口封闭,且对低频噪声的控制效果不好,故引入有源噪声控制技术降低室内声源通过开口的声辐射。基于惠更斯原理,均布开口的次级源和误差传声器构成的平面型虚拟声屏障可以实现对开口声辐射的有效控制,数值仿真和实验已证明其有效性。将次级源安装在开口边界更有利于保留开口的功能且方便实际安装,但这样的单层边界虚拟声屏障降噪效果存在上限,仅能在低频段实现全局控制。和单层边界次级源相比,双层边界次级源可显著提高降噪量和有效降噪频率上限。该文回顾了开口声辐射有源控制的相关工作,并讨论了未来可能的研究方向。     

平行声屏障的陷波模态及其插入损失优化

为了改善平行声屏障的性能，本文基于有限元仿真的方法对其陷波模态和插入损失进行了研究。其中，陷波模态是平行声屏障的固有性质，与其几何参数有关。当陷波模态处于共振频率时，平行声屏障内部声场的声能量达到峰值，同时声波垂直入射到声屏障的顶端，使声影区的衍射声能也达到峰值，最终导致插入损失显著下降。本文还对3种优化平行声屏障插入损失的方法进行了分析。结果表明，楔形和扩散型声屏障可降低声波的多次反射效应对插入损失的影响，但是对陷波模态的改善较小。而吸声型声屏障有效的抑制了陷波模态对插入损失的不利影响，从而改善了平行声屏障的性能。     

轻轨桥架声屏障降噪效果的测量与分析

在轻轨桥架两侧设置声屏障是控制轨道交通噪声的主要措施之一，对上海轻轨明珠线桥架两侧设置不同高度声屏障实际降噪效果的测量与分析，对声屏障的实用设计有重要的参考价值。     

虚拟声屏障在变压器低频降噪中的实验研究

针对开口房间内的变压器,在开口处布放若干扬声器和误差传声器构成虚拟声屏障,实验研究了虚拟声屏障对通过开口向外辐射的低频线谱噪声的控制效果。将15个次级源近似均匀分布在面积为2 m′ 2.7 m的开口面上,左右间距约58.5 cm、上下间距45-65 cm,15个误差传声器分别位于对应的次级源正前方1 m,系统采用自适应谐波降噪算法。结果表明：虚拟声屏障系统在误差点100 Hz、200 Hz和300 Hz的平均降噪量分别达到12.7 dB、19.9 dB和22.2 dB,虚拟声屏障对100 Hz、200 Hz、300 Hz线谱噪声的控制效果与单层封闭窗户相当,且内部合成参考信号,无需外接参考传声器。采用虚拟声屏障对开口房间内的变压器降噪的好处是实现室内外的自然通风,便于变压器的散热。     

计入地面附加衰减的声屏障插入损失估算方法*

基于理论推导和计算，给出了公路声屏障声学设计中，在考虑地面附加衰减情况下计算插入损失的方法。该方法综合考虑了有限长线声源无限长声屏障绕射声衰减量、有限长线声源地面衰减量及遮蔽角对插入损失的影响。通过与《声屏障声学设计和测量规范》（HJ/T90-2004）的计算结果的对比，验证了本文所给方法的精确性及可行性，并对规范所给地面衰减修正量进行了商榷。最后，给出了当预测点位于有限长路段中央法线上时，通过计算线声源地面衰减量得到计算插入损失所需参数值，再计算插入损失的简便方法。本研究为存在地面附加衰减情况下有限长声屏障插入损失计算提供了一个新的参考方法。     

高架桥声屏障高度对列车气动特性影响的数值模拟

采用计算流体力学方法对高架桥声屏障高度影响高速列车空气动力特性进行数值研究.通过网格划分、湍流模型选取、边界条件设置等来提高数值计算精度.结果表明,当高速列车运行在下风向时,头车、中间车上的侧向力随着声屏障高度增加而逐渐下降.头车所受的侧翻力矩在整车中最大,且随着声屏障高度的增加而逐渐减小.随着声屏障高度的增加,上风向工况下中间车受到的侧翻力矩要大于下风向工况.上、下风向工况下高速列车气动特性差异主要是由于流动空腔中列车所处的相对位置不同,改变了车体表面的压力分布,从而改变了车体所受到的气动力、力矩.     

预测声屏障插入损失的抛物方程法及其初始声场研究

Salomons建立的抛物方程(CNPE)方法可以预测非均匀环境中的声屏障插入损失。但是该方法在声屏障与声源距离较近时会产生较大误差。文中通过理论分析发现产生该问题的原因在于CNPE方法所使用的Gauss初始场仅适用于小仰角(10°以内)范围内的声波。为解决Gauss初始场引起的问题,推导了可以用于较大仰角声波的更高阶数的Gauss初始场。通过数值仿真对比了不同阶数的初始场在CNPE方法中的效果。结果表明:4阶初始场是最适合CNPE方法的初始场,将该初始场与CNPE方法相结合,可以准确预测当声屏障与声源距离较近时的插入损失.      

道路桥上一定长度全封闭声屏障成果通过市级鉴定

2005年9月15日由上海市经委主持对中国船舶工业第九设计研究院研究设计、宜兴强洁防噪声工程有限公司施工安装的道路桥上设置一定长度全封闭声屏障通过了科技成果鉴定。该段声屏障安装于南京惠民三期跨线桥上,系全封闭结构,长约140m,宽18．5m,     

有源声屏障中误差传感器的位置优化

有源声屏障利用有源控制系统提高声屏障低频段的降噪效果。有源控制系统中误差传感器的位置对整个系统的降噪效果有较大的影响。通过数值模拟和实验研究误差传感器的位置优化问题,得出了有源控制系统中误差传感器摆放位置的两条结论:(1)所介绍的三种摆放中,误差传感器的位置在次级声源的正上方时,有源控制系统在屏障后方声影区引入的新增插入损失最好,特别是对于距离屏障较远的区域;(2)当误差传感器的位置在次级声源的正上方时,误差传感器与次级声源间的距离存在一个最优距离使得屏障后方声影区的衍射声得到最好的降低。     

充液管路系统流体声与结构声的复合有源控制

采用基于谐频自适应控制算法的有源消声与消振系统对充液管路系统突出的低频线谱噪声进行有源控制实验研究.建立了泵水循环管路实验系统,在管路中安装有源消声器对流体声进行控制,在管路出口障板上采用8×8通道有源消振系统控制结构声辐射。开展的低频线谱噪声与振动有源控制实验结果表明,在50~200 Hz频带内,通过结合有源噪声与振动控制可在多数频点取得10 dB以上的降噪效果。针对该实验系统,通过分别控制流体声和结构声分析了两者的贡献.实验结果验证了有源消声与消振系统具有较好的降噪性能,各频点处流体声与结构声占比情况不同,需要综合控制流体声与结构声才可以取得显著的降噪效果。      

Acoustical barrier for tonal noises

In this paper, a novel acoustical barrier based on the principle of the Helmholtz resonator is proposed for the mitigation of tonal noises and its in situ performance has been assessed in comparison with a reflecting barrier and an absorbent barrier. For a lightly damped thin-walled reflecting barrier, the energy transmitted through the barrier structure is comparable with that diffracted over the edges. The absorption treatment not only absorbs acoustical energy but also damps the barrier structure resulting in a negligible energy transmission. The results demonstrated that for tonal noises the proposed barrier is more effective than reflecting and absorbent barriers.     

An active noise barrier with unidirectional secondary sources

An active noise barrier with unidirectional secondary sources is investigated in this paper, where the unidirectional secondary source consists of two closely located loudspeakers with pre-adjusted phase difference. The secondary sound field of the unidirectional sources is adjusted to maximally match the primary sound field in the shadow zone behind the barrier. It is shown both numerically and experimentally that the noise reduction performance of the active noise barrier can be improved remarkably by replacing monopoles with the unidirectional sources. The mechanism for the improvement is also investigated.     

Study on the analogy feedback active soft edge noise barrier

It is feasible to enhance the effect of reduction of the noise barrier on low frequency noise using the active control system. On the basis of the forerunners’ research, an analogy feedback active control system that is easy to be carried out was arranged on the top of a noise barrier to form an analogy feedback active soft edge noise barrier in order to enhance the effect of reduction of the noise barrier on low frequency noise. Through a preliminary experimental study, this method was proved to be feasible and the following preliminary conclusions on the arrangement of active control systems were made: (1) when control sources were arranged in a single row, the control effect was determined by the density of arrangement: the higher the density, the better the control effect; (2) with the same density of arrangement, the control effect of the double row arrangement was better than that of the single row arrangement; (3) with the same number of control sources, the single row arrangement had better control effect than the double row arrangement.     

Performance of an independent planar virtual sound barrier at the opening of a rectangular enclosure

Planar virtual sound barrier systems have been used successfully to reduce noise radiation through an opening without affecting natural ventilation and lighting. However, the complexity of a fully coupled control system grows at the rate proportional to the square of the number of channels and this make the system implementation become impractical for enclosures with large openings. To reduce the system complexity, this paper proposes an independent planar virtual sound barrier, which is a multi-channel system consisting of many independent single channel active noise control systems. Each single channel system is “independent” in the sense that the control source output of the system is updated only with the signal from its own error sensor. Based on the analytical model of sound radiation through the opening of a rectangular enclosure, the transfer functions from both primary and control sources are calculated first. Then the noise reduction performance, the stability, and the convergence behavior of both fully coupled and independent planar virtual sound barrier systems are investigated. It is found that the independent system with no control output constraint becomes inherently unstable at some frequencies; however its stability can be improved by applying some control output constraint. Reducing the number of channels and the distance between secondary loudspeakers and error microphones can also increase system stability but at the cost of smaller noise reduction. When the system is inherently stable and there is no constraint on control output, the independent system can provide the same noise reduction as the fully coupled one but with faster convergence speed.     

论一维方势垒穿透

量子隧穿是量子力学中一种重要的量子现象,本文对一维方势垒穿透问题作了全面的讨论,并统一了现行量子力学教材中3种不同情况(即:粒子能量E＞势垒高度V0、E＜V0和E=V0)的解.引入“约化势垒”,讨论了一些极端条件下一维方势垒穿透的物理现象.     

Schottky barrier MOSFET structure with silicide source/drain on buried metal

In this paper, we propose a novel Schottky barrier MOSFET structure, in which the silicide source/drain is designed on the buried metal （SSDOM）. The source/drain region consists of two layers of silicide materials. Two Schottky barriers are formed between the silicide layers and the silicon channel. In the device design, the top barrier is lower and the bottom is higher. The lower top contact barrier is to provide higher on-state current, and the higher bottom contact barrier to reduce the off-state current. To achieve this, ErSi is proposed for the top silicide and CoSi2 for the bottom in the n-channel ease. The 50 nm n-channel SSDOM is thus simulated to analyse the performance of the SSDOM device. In the simulations, the top contact barrier is 0.2e V （for ErSi） and the bottom barrier is 0.6 eV （for CoSi2）. Compared with the corresponding conventional Schottky barrier MOSFET structures （CSB）, the high on-state current of the SSDOM is maintained, and the off-state current is efficiently reduced. Thus, the high drive ability （1.2 mA/μm at Vds = 1 V, Vgs = 2 V） and the high Ion/Imin ratio （10^6） are both achieved by applying the SSDOM structure.     

Performance analysis of the virtual sound barrier system with a diffracting sphere

Since a practical virtual sound barrier (VSB) system has to be implemented surrounding a human’s head, the effects of such a diffracting sphere on the performance of the system are considered in this paper. It is found that the performance of the VSB system with a diffracting sphere might be improved or decreased depending on the size of the zone surrounded by the error sensors and the noise frequency, and the noise reduction distribution around the sphere tends to be uniform due to the diffraction of the sphere. Numerical simulations show that the tendency of the control performance with respect to the configuration of the system with a diffracting sphere is similar to that without the sphere. The diffracting sphere might move in the quiet zone of the VSB system, and the performance decreases with the increase of the distance between the sphere and the center of the system. However, the noise reduction level can remain more than 10 dB even when the sphere is near the border of the quiet zone. Experiments with a 16-channel cylindrical VSB system in a normal room validate the above conclusions.     

静电放电对功率肖特基二极管I-V及低频噪声特性的影响

本文基于人体放电模型分别对肖特基势垒二极管的阴极和阳极进行同一电压脉冲下的多次放电, 利用热电子发射理论、1/f噪声的迁移率涨落模型和白噪声理论, 分别深入研究静电放电损伤对器件I-V和低频噪声的影响. 结果表明, 静电放电作用于肖特基二极管阴极时损伤更严重, 噪声参量变化率更大. 随着放电次数的增加, 正向特性无变化, 反向电流总体增大, 偶有减小; 而正向和反向 1/f噪声均增大. 鉴于噪声与应力条件下器件内部产生的缺陷与损伤有关, 且更敏感, 故可将低频噪声特性用作肖特基二极管的静电放电损伤灵敏表征工具.     

Effect of a barrier potential on soliton dynamical characteristics in condensates

By using the multiple-scale method,this paper analytically studies the effect of a barrier potential on the dynamical characteristics of the soliton in Bose-Einstein condensates.It is shown that a stable soliton is exhibited at the top of the barrier potential and the region of the absence of the barrier potential.Meanwhile,it is found that the height of the barrier potential has an important effect on the dark soliton dynamical characteristics in the condensates.With the increase of height of the barrier potential,the amplitude of the dark soliton becomes smaller,its width is narrower,and the soliton propagates more slowly.     

A1/Ti/4H-SiC Schottky barrier diodes with inhomogeneous barrier heights

This paper investigates the current-voltage （I-V） characteristics of Al/Ti/4H-SiC Schottky barrier diodes （SBDs） in the temperature range of 77 K-500 K, which shows that Al/Ti/4H SiC SBDs have good rectifying behaviour. An abnormal behaviour, in which the zero bias barrier height decreases while the ideality factor increases with decreasing temperature （T）, has been successfully interpreted by using thermionic emission theory with Gaussian distribution of the barrier heights due to the inhomogeneous barrier height at the A1/Ti/4H-SiC interface. The effective Richardson constant A＊ = 154 A/cm2 . K2 is determined by means of a modified Richardson plot In（I0/T2） - （qσ）2/2（κT）2 versus q/kT, which is very close to the theoretical value 146 A/cm2 · K2.